#include <cmath>
#include "perlin.hpp"

/**
 * Structure permettant de définir le bruit de Perlin. Le bruit de
 * Perlin est un bruit cohérent, ce qui veut dire que ce n'est pas un
 * bruit totalement aléatoire, ce qui donnerait comme résultat de la
 * "neige".
 *
 * @author Jean-Marc Comby + Romain Dequesne
 *
 * @date 2004
 */
struct perlin
{
  /**
   * Tableau de nombre représentant une permutation de 512.
   */
  int p[512];
  perlin(void);
  static perlin & getInstance()
  {
    static perlin instance;
    return instance;
  }
};

/**
 * Permutation permettant de définir un bruit cohérent.
 */
static int permutation[] =
  { 151,160,137,91,90,15,
    131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
    190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
    88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
    77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
    102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
    135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
    5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
    223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
    129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
    251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
    49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
    138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180
  };

/**
 *
 */
static double fade(const double& t) 
{ 
  return t * t * t * (t * (t * 6 - 15) + 10); 
}

static double lerp(const double& t, const double& a, const double& b)
{ 
  return a + t * (b - a); 
}

static double grad(const int& hash,
		   const double& x, const double& y, const double& z)
{
  int h = hash & 15;                      // CONVERT LO 4 BITS OF HASH CODE
  double u = h<8||h==12||h==13 ? x : y,   // INTO 12 GRADIENT DIRECTIONS.
    v = h<4||h==12||h==13 ? y : z;
  return ((h&1) == 0 ? u : -u) + ((h&2) == 0 ? v : -v);
}
   
double noise(double x, double y, double z)
{
  perlin & myPerlin = perlin::getInstance();
  int X( static_cast< int >( floor(x) ) & 255 ), // FIND UNIT CUBE THAT
    Y( static_cast< int >( floor(y) ) & 255 ),   // CONTAINS POINT.
    Z( static_cast< int >( floor(z) ) & 255 );
  x -= floor(x);                                // FIND RELATIVE X,Y,Z
  y -= floor(y);                                // OF POINT IN CUBE.
  z -= floor(z);
  double u( fade(x) ),                                // COMPUTE FADE CURVES
    v( fade(y) ),                                // FOR EACH OF X,Y,Z.
    w( fade( z ) );
  int A( myPerlin.p[ X ] + Y ), AA( myPerlin.p[ A ] + Z ),
    AB( myPerlin.p[ A+1 ] + Z ),      // HASH COORDINATES OF
    B( myPerlin.p[ X+1 ] + Y ), BA( myPerlin.p[ B ] + Z ),
    BB( myPerlin.p[ B+1 ] + Z );      // THE 8 CUBE CORNERS,

  return lerp(w, lerp(v, lerp(u, grad(myPerlin.p[AA  ], x  , y  , z   ),  // AND ADD
			      grad(myPerlin.p[BA  ], x-1, y  , z   )), // BLENDED
		      lerp(u, grad(myPerlin.p[AB  ], x  , y-1, z   ),  // RESULTS
			   grad(myPerlin.p[BB  ], x-1, y-1, z   ))),// FROM  8
	      lerp(v, lerp(u, grad(myPerlin.p[AA+1], x  , y  , z-1 ),  // CORNERS
			   grad(myPerlin.p[BA+1], x-1, y  , z-1 )), // OF CUBE
		   lerp(u, grad(myPerlin.p[AB+1], x  , y-1, z-1 ),
			grad(myPerlin.p[BB+1], x-1, y-1, z-1 ))));
}

perlin::perlin() 
{ 
  for (int i=0; i < 256 ; i++)
    {
      p[256+i] = p[i] = permutation[i];
    }
}
